Preheat an outdoor grill on medium heat, and lightly spray the grate with cooking oil.

Combine the ground buffalo/beef, Worcestershire, and seasonings in a medium bowl. Knead together with your hands until well combined, then form the mixture into 8 equally-sized balls. Flatten them to make thin patties.

Divide the feta cheese between four patties, then top each with a second patty. Press the edges together to seal the cheese inside, then smooth out the sides with the palms of your hands. Sprinkle generously with salt.

Cook on the grill until the burgers are cooked to your desired doneness, 4-5 minutes per side for medium. Aim for between 145 and 160 degrees F. Remove from the grill and top with Havarti cheese, allowing it to melt from the residual heat. Let the burgers rest 4-5 minutes while you prep your toppings.

Place buns, cut side down, on grill and toast about 1 minute.

Load up the burgers! Layer arugula, red pepper, and red onion on the bottom on the hamburger bun. Top with the burger, bacon, and avocado. Spread some whipped feta on the cut side of the top buns, then place it on top of the burgers. Skewer with a toothpick or cocktail stick & serve.

Whipped Feta: Add crumbled feta to a food processor and pulse until small crumbs remain. Add cream cheese and puree for 4-5 minutes until creamy, scraping down the sides as necessary. Refrigerate any leftovers.